The roof on my house was replaced several months ago, right before I bought it. The realtor told me that moisture had come through the wall, and they realized it was a leak in the roof, which was then replaced. I've been replacing the baseboards throughout the house, and when I removed the baseboard below where the leak had been, I found mold:

As you can see, it's on both sides of that small protruding wall that comes out from the exterior wall. Do I need to tear all that down and see how extensive it is? Should I just assume it's a big problem and hire someone to take a look at it?

It hasn't bothered me, and presumably it's been there for the two months I've lived here. I wasn't sure if it was something that had to be completely removed at all costs, or just treated and contained. I would hope that the previous owner treated it before patching up the wall where the moisture came through. The only visible mold (on the outside of the wall) is behind the baseboard, so I can cut that out before replacing it.

Well I guess whether that mold is bad or not, give time to treat it or totally remove it on your wall. You know how molds can effect bad on our health right? What if it is not the only part that has the mold? Try to run some fans and dehumidifiers. Dehumidifiers can definitely help you on mold problems.

I'm aware that it can affect health, which is why I'm wondering how far I need to go to check it out. I really know nothing about treating mold, or what steps are recommended when a seemingly small amount like this is discovered. I'm hoping that when the wall was repaired where the leak came through, the previous owner had it treated and dried out. I can't be sure, which is why I'm wondering if I need to tear the drywall down in that area. I'll definitely look into the mold test kit.

If there is fiberglass insulation in the wall, repmove it and replace the insulation with something better.

Fiberglass will hold moisture, even though the glass fibers themselves do not absorb it. Any appreciable amount of moisture will dramatically reduce the insulation values by over 50%. The treatments typically kill only the active mold and not the spores, so the moisture remaining will allow them to sprout and go through the process again. Blowing air on fiberglass with a fan does not really dry it out. - It needs to removed, disturbed and fluffed, but spores may remain, but is cheaper and better to replace it.